An example of a conventional photoelectric conversion device includes a solar cell in which a boron (B)-doped p-type semiconductor layer and a collecting electrode patterned into a thin shape on the p-type semiconductor layer are formed, in the order they appear in this sentence, on one surface side of the crystalline semiconductor substrate, a phosphorus (P)-doped n-type semiconductor layer and a collecting electrode formed over the entire surface of the n-type semiconductor layer are formed, in the order they appear in this sentence, on the other surface side of the crystalline semiconductor substrate, and photovoltaic power is generated between the crystalline semiconductor substrate and the p-type semiconductor layer by the incident light from one surface of the crystalline semiconductor substrate. Another example of a conventional photoelectric conversion device is a heterojunction solar cell in which intrinsic semiconductor layers, thin-film semiconductor layers, respectively, doped with boron (B) and phosphorus (P), and transparent electrodes are used, instead of doping the semiconductor substrate with boron (B) or phosphorus (P).
In such photoelectric conversion devices, a metal material having no optical transparency is used for the collecting electrodes. Therefore, the light blocked by the collecting electrode on the light receiving surface does not contribute to the photovoltaic power. In other words, part of the light incident on the photoelectric conversion device is lost. Thus, in order to improve the power generation efficiency of the photoelectric conversion device, it is necessary to reduce the light blocked by the collecting electrode as much as possible.
In contrast, if the width of the collecting electrode is reduced in order to reduce the light blocked by the collecting electrode on the light receiving surface, the electrical resistance of the collecting electrode increases. If the electrical resistance of the collecting electrode increases, the efficiency of collecting the charge generated by light irradiation decreases. Consequently, even if the percentage of light blocked by the collecting electrode is reduced and the power generation current is increased, the fill factor of the photoelectric conversion device decreases due to the increase of the electrical resistance of the collecting electrode. Therefore, an adequate improvement of the photoelectric conversion efficiency cannot be expected.
In order to solve such problems, for example, in Patent Literature 1 and Patent Literature 2, the photoelectric conversion devices are a back-contact type in which all the electrodes are formed on one surface side of the semiconductor substrate, thereby eliminating the light blocked on the light irradiation surface and increasing the power generation current. The p-type electrode and the n-type electrode formed on one surface side of the semiconductor substrate are interdigitated so as to reduce the resistance between the electrodes. Moreover, what is called a front surface field (FSF) layer is formed on the light irradiation surface side on which an electrode is not present by doping with P that is of the same polarity as that of the crystalline semiconductor substrate, thereby returning the charge generated by light irradiation into the semiconductor substrate and thus reducing the recombination loss of the charge in the surface.